possible JB-Weld replacement

I'm getting ready to put my whole extruder together, and one thing I don't like about the current design is the suboptimal use of JB-weld. I'd prefer not to do something that can't easily be reversed if I make a mistake, and by some accounts it breaks down over time at the high temps used in the extruder. People have tried several alternatives (BBQ paint, other epoxies, I think nophead's got some sort've concrete stuff?) but none seem much better.

Has anyone tried holding on the heating wire/thermistor with PTFE tape? It seems cheap, plentiful - you can get it at any hardware store. According to this website: [www.hardwareandtools.com] it's good up to 500

Kyle Corbitt Wrote:
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>
> Has anyone tried holding on the heating
> wire/thermistor with PTFE tape? It seems cheap,
> plentiful - you can get it at any hardware store.
> According to this website:
> [www.hardwareandtools.com]
> base it's good up to 500

Has anyone tried low fire clay? Mold it around the barrel, wrap everything in fiberglass insulation, then run the nichrome heater for 8 hours on high to fire it?

Nophead quite some time ago started delving into this question and discovered an expensive, but very good material.

[hydraraptor.blogspot.com]

At the time I did a google search and discovered a few equivalents at much better prices in the US which may or may not have been as good as what Nophead found.

What it is is basically the cement that is used to surround nichrome heaters in heated probes like those used in stoves and electric hot water heaters as best as I can see.

Quote

Has anyone tried low fire clay?

I'm sure someone has, but I can't for the life of me find any mention of it anywhere. I guess my search-fu is weak, or my brain is clogging up or something. Or maybe no-one has. I'm sure it wouldn't be too much effort to try.

Forrest Higgs Wrote:
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>
> At the time I did a google search and discovered a
> few equivalents at much better prices in the US
> which may or may not have been as good as what
> Nophead found.
>

Since it is time for me to build another extruder I need something better than BBQ paint. I did the search over again and found the supplier in New York state. I called them just now and they are matching what Nophead's Cerastil to their best equivalent. They're talking about $60/quart, but I haven't got a final price yet. I'm going to buy some as soon as I get a good price. I'll let you know what I bought.

talking about cerastil..
I took a look at the webpage and there's "cerastil AE"
[www.panacol.com]

AND it's much cheaper (22 Eur/kg)

'sid

Edited 1 time(s). Last edit at 07/17/2008 10:57AM by sid.

Nice try. Graphite is electrically conductive. Mind, you might want to use it as the heating element directly instead of the nichrome.

Uuups, my fault!

'sid

Yes there are lots of Cerastil adhesives, the one I used is H115. I guess it is quite specialist because half of the Google hits are related to my use of it.

---

[www.hydraraptor.blogspot.com]

Yet another high temperature cement is omegabond, about 40$ for a 8 fluid ounces (224 ml), whose specifications are at:
[www.omega.com]

For high temperature operation, you have to set this brand of cement at 105 C for four to twelve hours depending on the type, to get a final set. I haven't used it so I don't know how well it works.

The El Cheapo method is to use furnace cement. It has to be fired to get even slightly strong. The best instructions I found for casting concrete made of furnace cement and perlite were at:
[web.archive.org]

In that page John Wasser said someone reported the concrete on its own was slumping, so indeed it seems that it has low strength and can probably only be used as a supported insulator.

It's almost impossible to get concrete made with perlite dry. I had some graduate students trying to measure the thermal conductivity of perlite concretes years ago and there was always so much water in it, even after a long curing in the lab ovens that they got wonky measurements.

... it could be worth a test mixing talcum powder with water-glass ( [en.wikipedia.org] ) - both are good heat-resistant (talkum until 1600

Edited 1 time(s). Last edit at 07/17/2008 03:29PM by Viktor.

Another candidate, although possibly not on it's own is kapton.
[en.wikipedia.org]

It has a large temp range, -269

... you can have Polyimide (what Kapton is basically) as fluid too, which harden, when cured at >150

Forrest Higgs Wrote:
-------------------------------------------------------
>
> I did the
> search over again and found the supplier in New
> York state. I called them just now and they are
> matching what Nophead's Cerastil to their best
> equivalent. They're talking about $60/quart, but
> I haven't got a final price yet. I'm going to buy
> some as soon as I get a good price. I'll let you
> know what I bought.
>

Okay, the people at Cotronics suggested a substitute for Cerastil.

[www.cotronics.com]

I just bought a pint ($52.50 before shipping) which, if it is dry powder should be about a kg. It's considerably cheaper than what Nop bought and appears to have much the same formulation and characteristics.

I'll blog how it works out. It apparently sets very, very quickly.

Hrm. I'm new here, so hope this isn't too crazy.

I just took apart an old Radio Shack soldering iron for the nichrome to make my first rep(st)rap. The heater element was built by wrapping bare nichrome around a barrel similar to the extruder, but using what appears to be several layers of flexible mica material as the electrical insulator, both on the inside and outside of the coil. The nichrome appears to be tautly wound over the inside insulation, then held in place by wire wraps at the ends of the coil, with the outside wrapping to keep the protective sleeve (protection and shielding from breezes) from shorting the coil.

Could the extruder heater element use something similar? Mica's frequently used as an electrical insulator between electrical components and heatsinks because it has good thermal conductance. If the nichrome was tightly wound over the mica film, and then secured with tightly cinched wire wraps (which also form the connection points), it should be reasonably stable without needing JB-weld. A protective sleeve would finish the assembly.

Course, the thermistor might still need to be JB-weld'ed, or BBQ-painted on for good thermal conductance, but since it won't see the direct heat that the coil delivers it might survive okay...

David

I think that you will find that mica is a bastard to work with and hard to obtain in the amounts and quality you need to do the job. If you want to have a go with it, however, here is a supplier.

[www.k-mac-plastics.net]